The present invention relates generally to detection and location of ground faults in electrical power distribution systems, and more specifically to a technique for detecting and locating phase-to-ground faults in high resistance grounded power systems.
A ground fault is an undesirable condition in an electrical system, in which electrical current flows to the ground. A ground fault happens when the electrical current in a distribution or transmission network leaks outside of its intended flow path. Distribution and transmission networks are generally protected against faults in such a way that a faulty component or transmission line is automatically disconnected with the aid of an associated circuit breaker.
One grounding strategy for low voltage power systems is high resistance grounding. In high resistance grounded power systems, an impedance is provided between the neutral and ground of a source power transformer. This high resistance grounding allows continued operation of the power system even in case of single phase-to-ground fault. However, depending upon the system design, to permit such continued operation, the ground fault should be detected and located to relieve the extra voltage stress in the power system and also to remove the initial fault to eliminate the occurrence of series of faults from phase to phase.
Hand held sensors have been used to trace a fault in power systems. Conventionally, either a signal is injected at the grounding impedance or a portion of the grounding impedance is periodically partially shorted via a contactor. This produces a zero sequence current in the power system that can be traced using the hand held sensor. The hand held sensor must typically be placed encircling all the conductors at a selected measurement point in the power system, to indicate whether the measurement point is between the grounding impedance and location of the ground fault. The hand held sensor is moved from one point to another in the power system until the fault is located in this manner. The process is, however, time consuming and labor-intensive.
Accordingly, there is a need for a relatively straightforward and automated process for detecting and locating ground faults in an electrical power distribution system.